Welcome Learning:
You didn't mention the material the vent line or gas line are made of. If the vent is galvanized metal pipe and the gas line is black iron pipe, there is no problem. If your vent is aluminum and the gas line is copper they should be seperated because of the electrolisis between those two metals. You could also get some foam pipe insulation to put on the gas line to prevent contact.
Glenn

How Dangerous is this electrolisis thing. I keep hearing about it but the concept is hard to grasp. It seems like something plumbers say to sound smart. (no offense glenn i know youre smart) Have you actually seen the affects of electrolisis. how long does it take. it kind of makes sense if there is electric going through it but aluminum wires connect to copper wires pretty commonly with out concern.

Copper and aluminum are not connected anywhere, they need separation in electrical.
Electrical connections need to be UL rated for that specific connection due to moisture which causes an electrolyte issue, they even make wire nuts for this problem. Water lines are separated by a 4 inch or larger piece of brass or a specific connector in plumbing.
It all depends on what you are trying to do, moisture is the culprit. Have you realized that new pressure treated lumber can no longer be used with aluminum because of the copper treatment which is now used .

That is "dissimilar metals" in some of the building arena.
Google it and you will learn more than you need.

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Last edited by inspectorD; 01-22-2008 at 06:50 PM.
Reason: Galvanic corrosion of the brain.